Cylinder head for a four stroke combustion engine

A cylinder head of a four stroke combustion engine with a valve gear with lifting valves, comprising:

• a cylinder head having at least one inlet conduit provided with a valve and at least one exhaust conduit joining into a single main conduit, the main conduit having an orifice opening into a cylinder, the orifice having a cross-section in the shape of an annulus, an axis of the orifice being aligned with a main axis of the cylinder and the orifice of the main conduit being provided with an interior valve seat and an exterior valve seat,
• a sole lifting valve having an annular plate disposed in the cylinder, the lifting valve having a closed position in which the annular plate is seated on the interior valve seat and the exterior valve seat,
• wherein the exhaust conduit of the cylinder head is directly interconnected to an exhaust branch and provided without any valve gear, where the orifice defines a flow cross-sectional area is substantially equal to a sum of an outer flow cross-sectional area defined between an outside diameter d.sub.2v of the annular plate and an inner surface of the cylinder and an inner flow cross-sectional area defined within an inside diameter d.sub.1v of the annular plate and wherein a ratio of the inside diameter d.sub.1v of the annular plate to the outside diameter d.sub.2v of the annular plate is substantially equal to a ratio of the inner flow cross-sectional area to the outer flow cross-sectional area, wherein the lifting valve is provided with at least one stem and wherein the cylinder head includes a space adjacent the interior valve seat, at least one of a sparking plug and an injection nozzle being disposed in the space.